computers -...

CSE120, Spring 2017L13: Computers

ComputersCSE 120 Spring 2017

Instructor: Teaching Assistants:Justin Hsia Anupam Gupta, Braydon Hall, Eugene Oh, Savanna Yee

Steve Jobs’ custom Apple I and other historic machines are on display at Seattle museumIn the earliest days of those early days, Steves Wozniak and Jobs made their first device together: the Apple I. Few of these were sold, and fewer still survive — but the Living Computers museum in Seattle managed to get three. And one of them was Jobs’ personal machine.That’s the mission of the museum, though: the Apple I, along with dozens of other ancient computers… are deliberately there to be touched and, if not truly understood, at least experienced.

• https://techcrunch.com/2017/04/17/steve‐jobs‐custom‐apple‐i‐and‐other‐historic‐machines‐are‐on‐display‐at‐seattle‐museum/


Administrivia

Assignments: Creativity Assignment (4/24) Reading Check 5 (4/27)

Midterm in class on Wednesday (4/26) Bring 1 sheet of notes (2‐sided, letter, handwritten) Fill‐in‐the‐blank(s), short answer questions, multiple choice

• Questions 1‐7 on readings and big ideas (drop 2 lowest scores) [10 pt]• Questions 8‐10 on computational thinking (code: reading, writing, and debugging) [20 pt]

Time is not your friend• Short answers should be short• Skip questions and come back later

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Living Computers Museum Report

Due Sunday, May 14 You have weeks 5‐7 to complete

Required to visit the Living Computers Museum in SODO 2245 1st Avenue South, Seattle, WA 98134 Your admission has been paid for! (transportation is not) Lots of hands‐on exhibits involving old computers and modern gadgets

and other big ideas from CSE120 We encourage you to visit in groups!

Worksheet to complete after visit Involves some photos, a little bit of research, and some written

responses

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Outline

Student Work Showcase Computer Components Computer Instructions Instruction Execution

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Jumping Monster

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Jack CummingsAliakesi Zhuranko


Outline


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Computers are Complex

7http://xkcd.com/676/


Audience Responses

What are different computer components you’ve heard of? Hard drive RAM (memory) CPU (processor) Monitor Graphics Card Motherboard Keyboard Mouse Speakers Etc…

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Five Components of a Computer

Control Datapath Memory Input Output

Processor

Computer

Control

Datapath

Memory Devices

Input

Output

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Input

Devices that send information to the computer

Examples we’ve seen: Mouse Keyboard Ethernet cable/wireless card

Other examples: Microphone External sensors Disk (read)

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Output

Devices that the computer sends information to

Examples we’ve seen: Monitor/graphics card Ethernet cable/wireless card

Other examples: Speakers Printers Disk (write)

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Memory

Place for temporary data storage Typically random access memory (RAM) Data is lost when the computer loses power! Permanent storage goes to disk

Needed by programs as they run Running out of available memory is typically what causes your computer to slow down

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Central Processing Unit (CPU)

The “brain” of the computer – the circuitry that carries out the instructions Datapath – all of the hardware components needed to handle all possible instructions Control – the routing (decision‐making) that determines correct instruction execution

Confusingly, modern CPUs contain multiple processors that can each run multiple processes simultaneously More on this in a later lecture

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Computer Internals: Physical View

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CPU(empty slot)

USB, etc.

I/Ocontroller

Storage connections

Memory


The Operating System

Everything mentioned up to this point was hardware

The piece of software that ties everything together and coordinates between hardware and software is the operating system (OS) It’s a program, just like everything else, but more important The OS has special privileges The OS is heavily responsible for the security of your computer (programs and data)

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Outline


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What Does an Instruction Look Like?

Just like all other data on a computer, instructions are also just binary data!

Example: 0x4801FE tells my computer to add one number to another Similar to x = x + y;

An executable (program) contains the binary encoding of all of its instructions and data Plus some other information Hex view demo [see Panopto]

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Limited Instructions

The number and type of instructions is always limited

The agent can only do certain pre‐defined actions

In a computer, this is determined by the Instruction Set Architecture (ISA) The CPU and other hardware is designed to execute onlythese instructions

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Types of Instructions

1) Perform arithmetic operation in the CPU c = a + b; z = x * y; i = h && g;

2) Control flow: what instruction to execute next Normally whatever instruction comes next in sequence Jump to function calls Possibly jump on conditional branches Possibly jump for loops

3) Transfer data between the CPU and memory Load data from memory into CPU Store CPU data into memory

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How Can We Get Away With This?

Most computation handled by CPU, but it can only hold a small amount of information at a time For reasons of cost and speed

As needed, transfer data between CPU and Memory As an added trick, treat all Input and Output “like memory”

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CPU Memory

Disks Net USB Etc.

Interconnection Bus


Memory

We can think of memory as a single, massive array Every memory entry is the same size (1 byte) Every memory entry has an index (memory address) and a value (data)

If our computer instructions need to use data that is stored in memory, it can reference it by using the correct memory address

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A7 00 32 00 00 FA • • • CE 26 F4 DE AD 96Address (hex):

Value (hex):

Memory


Where are the Instructions?

When a program is running, the instructions for that program are stored in memory Faster to read instructions from memory than from executable file on disk

The CPU reads instructions for execution in the exact same way that it reads data from memory Take advantage of existing hardware

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Generating Instructions

Must learn how to specify complex tasks using just these simple actions In reality, this is often done automatically for us:

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Higher‐Level LanguageProgram (e.g. Processing)

Assembly Language Program (e.g. x86‐64, MIPS)

Machine Language Program(executable)

Compiler

Assembler

temp = v[k];v[k] = v[k+1];v[k+1] = temp;

0000 1001 1100 0110 1010 1111 0101 10001010 1111 0101 1000 0000 1001 1100 0110 1100 0110 1010 1111 0101 1000 0000 1001 0101 1000 0000 1001 1100 0110 1010 1111

lw $t0, 0($2)lw $t1, 4($2)sw $t1, 0($2)sw $t0, 4($2)


Outline


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Instruction Execution

The agent follows the instructions flawlessly and mindlessly A computer will follow the instructions given by a program and should produce identical results if given identical inputs

The CPU knows where to find the next instruction using the program counter (PC) PC contains the address of the next instruction in memory PC gets updated after each instruction is executed, sometimes jumping around based on the program’s control flow

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Fetch‐Execute Cycle

The most basic operation of a computer is to continually perform the following cycle:1) Fetch the next instruction (read from memory)2) Execute the instruction based on its purpose and specified

data

Furthermore, the Execution portion can be broken down into the following rough steps:1) Instruction decode2) Data fetch3) Instruction computation4) Store result

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Machine: 0x4801FEAssembly: add %rdi, %rsi


Arithmetic and Logic Unit (ALU)

A special logic block that is part of the CPU and performs the arithmetic operations Performs the operations needed to cover all the instructions that the CPU can understand Typically limited to two operands, which restricts the overall instruction set

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Computer Components Revisited

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Clock Rate

The rate at which your CPU can perform a Fetch‐Execute cycle Must make sure that clock speed is slow enough to accommodate the slowest instruction

Clock rate is usually given in Hertz (Hz = second‐1) Example: 2 GHz = one instruction every

= Clock rate is not a good indicator of speed

• CPU must often wait for data from memory or I/O devices

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Example: Running a Processing Program

1) The Processing environment compiles your code into machine language Your Processing code gets converted into machine code (just 0’s and 1’s)

2) When you run the program, memory is allocated for the program’s instructions, variables, and data

3) Starting from the beginning (setup(), in this case), the computer will perform the Fetch‐Execute cycle Keeps going unless end of program is reached or an error is encountered before then

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